The Sutton Hoo Saxon Ship – Development and Analysis of a Computer Hull Model Prior to Full Scale Reconstruction
Total Page:16
File Type:pdf, Size:1020Kb
Historic Ships, 7-8 December 2016, London, UK THE SUTTON HOO SAXON SHIP – DEVELOPMENT AND ANALYSIS OF A COMPUTER HULL MODEL PRIOR TO FULL SCALE RECONSTRUCTION P Handley, Paul Handley Design, UK SUMMARY This paper reviews recent research prior to a planned full-size reconstruction of the Saxon ship found at Sutton Hoo. The work included establishing the fundamental form of the ship by reviewing available historic information and data with consideration to possible distortion due to movement of ground and decay of timbers and likely units of measurements used based on measurement of Saxon buildings. From this research a computer hull model was generated and hydrostatic and stability software used to assess the likely displacement, loading and stability characteristics. Performance under oar power was assessed with performance prediction software and a faired lines plan was generated from the computer model. The Woodbridge River Trust plan to commence construction of the full-size replica in 2017. 1. INTRODUCTION - A plan prepared by the Science Museum in 1939 showing the hull lines, section shape at frames and In 1939 an ancient burial mound was excavated near rivet positions for planking. A full copy of the plan is Sutton Hoo in Suffolk and the remains of an Anglo held at the Ipswich Museum and the plan is also Saxon ship uncovered. The ship was almost 27m (90ft) shown as Figure 135 in [1]. long, of wood clinker construction, propelled by up to 40 oarsmen and estimated to date to 625AD. - Information and observations recorded by Robert Bruce-Mitford and Angela Care Evans following the All of the original timber had decayed, but a well- 1967 re-excavation [1]. preserved impression of the plank and frame surfaces was left in the ground and the iron rivets remained in - Lines plans of the ship by Colin Mudie, one dated place. 1973 with hull sections at frame positions [1] and a second dated 1974, number 202.8 The excavation was cut short by the onset of war and little recorded data survives except for detailed - A plan showing planking and rivet positions, photographs of the ship impression and a provisional including a body plan with hull sections at frames, lines plan produced by the Science Museum in 1939. In (Figure 325 in [1]) described as an archaeological plan 1967 the site was re-excavated and further lines plans ‘based on 1939 photographic records and information drawn, but by then the hull impression had considerable gained by the 1967 re-excavation’. damage and the excavation team focused mainly on archeological aspects and construction. - Measurement data of the rivet positions taken in the 1967 re-excavation and a permanent record of the The available records and data were reviewed so that an 1967 shape taken via a glass fibre moulding taken to accurate computer model of the ship could be developed the British Museum to look at the stability and performance characteristics and to provide a lines plan for the planed full-scale No detailed measurement data of the shape of the reconstruction. impression in the ground in 1939 was available, nor any offset tables for the lines plans listed above. Detailed 2. HISTORIC DATA measurement data was taken in the 1967 re-excavation but by this stage the impression had been badly damaged. The recorded information, drawings and measurement data available for study for this work included: 3. OBSERVATIONS ON DATA - Extracts from notes from the 1939 excavation written 3.1 1939 PHOTOGRAPHS by C.W. Phillips and Commander Hutchison, in Volume 1 of the Sutton Hoo Ship Burial by Robert From the photos taken the first excavation in 1939, it can Bruce-Mitford [1]. be seen that the overall shape was preserved extremely well with the rivets showing the lines of plank edges and - Detailed photographs taken in 1939, which provide a some frames showing, although there were some areas of clear indication of the overall shape of the ship missing detail and local irregularities in shape. Figure 1 impression at that time. is one of several very clear photographs taken in 1939 by © 2016: The Royal Institution of Naval Architects Historic Ships, 7-8 December 2016, London, UK Miss B. Wagstaff. By studying the photos the following twist or angle of list, which are issues relating to the points can be observed regarding the shape of the ship: shape of the ship that were considered by the 1967 excavation team. Extreme ends - It can be seen from the photographs that no detail was uncovered at the extreme ends of the hull in The process of creating fair hull lines by hand through a 1939. Figure 2, a photograph of bow taken by C. set of unfair points would have been fairly time Phillips, shows this. The loss of the ends was probably consuming for the museum staff and they had little time due to the proximity to the ground surface and possible available to do this in 1939 due to the impending war. ploughing etc. Any drawings showing the bow or stern Accordingly the museum plan’s lines are not considered end extensions are not based on preserved evidence. to be a completely accurate record of the ship’s shape, particularly given that the ends of the ship are closer to Mid-sections - Not much detail of the shape or position the shape of the impression in the ground than to the of frames can be seen in the middle third of the length of shape that might have been expected for a ship of this the boat, but considerable detail of frame shapes was type and construction. preserved forward and aft of this middle section. Therefore, when interpreting the shape shown on any 3.3 1967 RE-EXCATVATION plans less emphasis was given to the middle sections than to the forward and aft thirds. In 1967 the Sutton Hoo ship mound was re-excavated to establish more information about the ship. Unfortunately Bow and stern sections - The photographs in Figure 2 the shape of the impression had by then been damaged shows that the bow sections of the ship impression were by military training exercises on the land during the war, flared out rather than the sharp and more vertical ends but is was still possible for the team to learn more about normally found on boats of this era, such as the Nydam the ship, in particular relating to construction and areas boat [2]. The same was true at the stern. of detail. The general consensus since the discovery of the Sutton All rivets on the site were collected and preserved after Hoo ship is that this shape at the ends was probably their measurement positions had been recorded and caused by the planks springing away from the stem and eventually a full-scale glass-fibre casting was made of stern posts. This could be explained if the sand and soil the impression. This was made in sections to allow used to back-fill the cavity outside the hull when it was transport to be stored at the British Museum. Figure 4 buried compacted downwards over time, reducing the shows the casting assembled. support of the planks ends near the top of the mound. As the ends were near the ground surface and may have Although the casting has a boat shape, it is distorted extended beyond the surface, decay of some timbers locally and missing much of the top-sides due to the would have been faster here reducing support and damage to the impression during the war, such that both allowing the planks to move. Rupert Bruce-Mitford and Angela Care Evans stated that the re-excavation did not provide information on the Topsides - The spreading outwards of the bow and stern overall shape of the boat that could improve on that planking would have extended at least some way towards recorded by the museum plan. the middle of the boat, so throughout the length of the boat there may have been some slight outward movement 3.4 PLANS POST 1967 of the top planks as the soil settled. There seems to be some evidence of this shown in the photos. Several more provisional lines plans of the ship were drawn after the 1967 re-excavation, based on the data 3.2 SCIENCE MUSEUM 1939 PLAN available from both excavations. At least two lines plans were prepared by the Colin Mudie design office and a A plan was drawn in 1939 by the Science Museum, part further plan was produced illustrating the planking and of which is shown in Figure 3. The plan, which was some other construction detail. labelled as ‘provisional’, shows longitudinal lines and sections following fair curves without the local The section lines shown in the Science museum plan irregularities in shape that can be seen in the photos. It were compared with the later lines plans and it could be therefore seems reasonable to assume that when the plan seen that they all varied in shape. The 1973 Colin Mudie was produced, fair curves were drawn as a best fit plan showed finer sections throughout the length of the through the measurement data that was recorded at the boat than the Science Museum plan. The 1974 Mudie time. plan showed significantly fuller sections than the 1973 plan, closer to the shape shown in the Science Museum Although not stated, it is likely that measurements taken plan. Figure 5 shows a comparison of the 1973 Colin from both sides of the ship impression were averaged for Mudie body plan and the museum plan – the fine lines this exercise, thus eliminating concerns over asymmetry, are from the Colin Mudie plan.